We have shown that weight reduction improves insulin sensitivity and insulin secretory response to oral gluocose in obese normal and diabetic subjects. Further studies designed to help elucidate the relationship of Type II diabetes to obesity have employed insulin therapy and exercise training. Short term (10 days) insulin therapy was shonw to have no effect on sensitivity to insulin as measured by the glucose clamp technique, however, there was an improvement in the blunted insulin response to oral glucose. Six to tweleve weeks of aerobic bicycle exercise resulted in improvement in maximal oxygen uptake capacity in obese normal, glucose intolerant and diabetic subjects. Exercise training resulted in improvement in insulin sensitivity in normal, glucose intolerant and mildly diabetic subjects, but no improvement was seen in moderately diabetic subjects. On the other hand, oral glucose tolerance improved in all diabetic subjects and could be attributed in part to an improvement in the early insulin response with exercise training in the diabetics.